Field of the Invention
The present invention relates to an image decoding device, and more particularly, to a device that uses quantization parameters of left and top coding units to derive a quantization parameter predictor used for generating a residual block.
Discussion of the Related Art
Image data has to be encoded to efficiently store or transmit the image data. MPEG-1, MPEG-2, MPEG-4, H.264/MPEG-4 AVC (Advanced Video Coding), and the like are known as techniques of encoding image data. In these techniques, a picture is divided into macro blocks, it is determined which of intra encoding or inter encoding should be performed in the unit of the macro blocks, and the macro blocks are encoded using the determined encoding method.
In H.264 which is a latest image compressing technique, intra prediction is performed to enhance the efficiency of the intra encoding. That is, instead of referring to a reference picture to encode a current block, a prediction block is created using pixel values spatially neighboring the current block to be encoded. Specifically, an intra prediction mode having a small distortion is selected through comparison with an original macro block using the neighboring pixel values and the prediction block of the current block to be encoded is created using the selected intra prediction mode and the neighboring pixel values. A residual block including difference signals between the current block and the prediction block is created and the residual block is transformed, quantized, and entropy-encoded. The intra prediction mode used to create the prediction block is also encoded.
However, in H.264, the intra prediction mode of a current block is encoded regardless of directivity of the intra prediction modes of the left and top blocks of the current block and there is thus a problem in that the encoding efficiency is low. When the number of intra prediction modes increases to enhance the encoding efficiency of a residual block, there is a need for an intra prediction encoding method having efficiency higher than that of the intra prediction mode encoding method of H.264.
When coding units having various sizes are allowed unlike in H.264, a quantization parameter can be adaptively changed to improve encoding efficiency of a texture. However, in this case, a large number of bits are required to transmitting the quantization parameter. Therefore, there is a need for a method capable of effectively reducing the number of bits.